The expression design loads is understood to mean, within the context of the present invention, the maximum loads that can be supported by the structural parts taken into account (namely the fin) without permanent deformations appearing.
With the obvious aim of safety, an inspection of the fin of the aircraft, as well as the repair of any flaws, have to be performed as soon as said design loads are overstepped.
An inspection of structural parts of the aircraft is generally triggered following the generation by an incident detection computer, for example of the FWC (“Flight Warning Computer”) type, of a speed overshoot alarm (also known as an “overspeed warning”).
In general, such an alarm is tripped when an overshoot of more than four knots of a permitted maximum speed (Mach number) dependent on the current configuration of the aircraft, is detected.
The various maximum speeds (Mach numbers) are determined by virtue of load models specific to each zone of the aircraft, in such a way that the constituent elements of the aircraft do not undergo any structural load of such a kind as to damage them.
Such an overshoot of maximum speed (Mach number) may occur upon unusual maneuvers, upon encountering significant turbulence or upon erroneous actions on the part of the pilot.
The activation of this alarm compels the airline, in accordance with the maintenance manual, to perform a maintenance check of the aircraft. This operation is aimed at verifying the ability of the structure of the aircraft to properly withstand the loads encountered during the speed excursion (Mach number) beyond the flight domain.
This check consists in visually ascertaining that cracks/fissures have not developed and/or that structural elements or ties are not deformed and in verifying that the various systems potentially affected are still operating normally.
Such maintenance checks therefore keep the aircraft grounded, which of course penalizes the airline.
Moreover, statistical information originating from airlines points to a relatively significant frequency of occurrence of speed overshoot. In fact, for more round trips, airlines often ask their pilots to fly at speeds close to the maximum speeds. In consequence, a simple gust of wind or turbulence triggers the alarm, thereby compelling the airline to perform the maintenance check as described in the aircraft's maintenance manual.
Now, it is apparent that, in a very large majority of cases, no damage at the level of the structure of the aircraft of crack, fissure, etc. type has been observed. Thus, it is apparent that the criterion compelling or otherwise the carrying out of a maintenance check following a speed overshoot alarm of the aforesaid type, is excessive and unsuited to the requirement.